Someday your sweat might power your phone

UC San Diego researchers have developed a skin patch that monitors an athlete’s performance during workouts and generates electricity from the sweat. While the idea is still in its infancy, it could someday power such small personal electronics as heart monitors, watches — maybe even phones.

A skin patch developed by UC San Diego researchers monitors lactate levels in sweat and generates electricity at the same time. Photo: Joseph Wang, the American Chemical Society. Video: the American Chemical Society.

“We came up with this idea of harvesting energy directly from the body, in a non-invasive manner,” said Joseph Wang, chairman of the school’s nanoengineering program.

The patch, unveiled Wednesday in San Francisco at the annual meeting of the American Chemical Society, looks like a temporary tattoo. But it contains an enzyme that responds to lactate in sweat. Lactate is a byproduct of glycolysis, a process by which the body generates energy for physical activity. The harder the workout, the higher lactate levels rise.

Professional athletes sometimes analyze their lactate production while fine-tuning their training programs. But the process isn’t quick or simple, requiring blood samples. So Wenzhao Jia, a post-doctoral student in Wang’s lab, and several colleagues devised the patch, essentially a lactate sensor placed directly on the skin.

The enzyme contained within the patch strips electrons from the lactate, generating a tiny electrical current. The strength of the current shows how much lactate is present in the sweat. But the current could also be used for other purposes.

It isn’t much. The UC San Diego researchers tested the sensor on 15 volunteers pedaling on a stationary bike and found they generated a maximum of 70 microWatts per centimeter of skin. Hook the patch to a light bulb, in other words, and you’d get nothing.

Larger and better versions, however, could conceivably power wearable technology, as well as give athletes a useful tool for improving their workouts.

“The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices,” Jia said.